Multiple sclerosis (MS) is a chronic inflammatory disease characterized by lymphocyte infiltration and tissue destruction in the central nervous system (CNS). The myelin reactive T cells found in the blood and cerebrospinal fluid of MS patients re in a different state of activation as compared to T cells in normal individuals and thus are thought to be directly involved in the disease pathogenesis. Our long-term goal is to understand the molecular basis for the in vivo activation of autoreactive T cells in MS, providing the basis for rational therapeutic intervention. This project is based on the hypothesis that costimulatory molecules provide the second signal which activates autoreactive T cells which are required to induce autoimmune disease. As we have recently discovered increased expression of B7-1 in acute Ms lesion, the requirement for expression of B7-1 and B7-2 molecules and IL-12 by human glial cells will be examined. In the next aim, the molecular basis for the activated in vivo state of autoreactive T cells in MS patients will be further investigated by comparing myelin antigen-autoreactive peripheral blood T cells in MS patients to controls and determining their capacity to expand in response to antigen presented by CHO cells transfected with MHC class II, DR21, alone or with B7-1 or B7-2 costimulatory molecules and DR2. We will also examine regulatory role of B7-2 expressed on activated T cells, which may be of significance for the disturbed immunoregulation described in MS. Our preliminary data demonstrate that B7-2 expressed on T cells has a lower molecular weight than B7-2 expressed on B cells or CHO cells, and has lost its binding affinity for CD28 but not CTLA4. In our last aim, we will further investigate negative regulatory functions of B7-2 expressed on T cells in a novel CD8 anergy system. These aims will provide basic information on the role of costimulation and anergy induction in CD4 and CD8 T cells as it may apply to understanding immunoregulation of MS, a human autoimmune disease.